Respiratory viruses are a major cause of morbidity and mortality worldwide. After infecting their target cells, viruses are sensed by different pattern recognition receptors (PRR?s) that initiate innate anti-viral immune responses. Viral double stranded RNA (dsRNA) is a potent stimulator of innate immunity and activates toll-like receptor 3 (TLR3) as well as the intracellular helicases RIG-I (retinoic acid-inducible gene I) and MDA5 (melanoma differentiation-associated protein 5). Double stranded RNA sensors are expressed by the airway epithelium, and couple to complex downstream signaling pathways that initiate the expression of interferons and cytokine genes, resulting in airway inflammation and induction of anti-viral immunity. This R01 application is based on our serendipitous discovery that the serine/threonine kinase protein kinase D (PKD) has a previously overlooked role in innate immune responses driven by the dsRNA polyI:C. There are three PKD isoforms (PKD1-3), but little is known about their expression or function in the lung. Using targeted siRNA knock-down and a new line of knock-out mice, we found that polyI:C-induced epithelial cytokine gene expression and neutrophil recruitment to the lung are both dependent on PKD3. This appears to involve a previously unreported role for PKD3 in polyI:C signaling in epithelial cells, as well as in chemokine receptor signal transduction in neutrophils. Excitingly, we also discovered that a potent and selective PKD antagonist protects mice from infection with influenza A virus (IAV). In this revised R01 application, we propose three Aims that will: explain exactly how PKD mediates dsRNA signal transduction in airway epithelial cells (Aim 1), use conditional deletion and other strategies to unravel a new neutrophil specific role for PKD3 in lung inflammation (Aim 2), and test the hypothesis that targeting PKD will attenuate lung inflammation after influenza infection in mice (Aim 3).